Girder bridges made from timber

Girder bridges are especially suitable for span widths of 5 to 20 m.

Most girder bridges are designed from two main girders which function as static bending beams. In this respect, the roadway surface runs over the supporting structure and therefore functions as a cover for the supporting structure at the same time. Since the main girders are thus protected under the road surface, the system provides the best requirements for an optimum structural timber protection with limited maintenance costs.

Girder bridges offer a good cost-benefit balance with a visually appealing appearance. They are frequently used as single span bridges.

Attributes of Girder bridges:

• Usually designed with two main girders made from laminated timber
• The roadway surface runs over the covered main supporting structure
• Design of the road surface in the form of solid timber decking or alternatively as a mastic asphalt surface
• Fitting of the railing on the side of the main girders, equipped with a cover decking on the top
• The casing on the top and side of the girders ensures the optimum protection against weathering

Protected main supporting structure

Structural timber protection is the key to the longevity of a timber bridge. Structural timber protection intends for all structural timber components to be completely protected. In this respect, the following steps are taken into consideration: Installation of technically dried timber with a timber humidity of 12% in order to prevent insect infestation, protection against weathering, ingress of moisture, UV rays due to the installation of projections and skirting in the design as well as good air circulation to encourage drying out. Constructions designed in this way satisfy the requirements of protected timber bridges pursuant to DIN EN 1995-2 NA. This means that loss events are prevented and maintenance costs are minimised, and the use of timber preserving chemicals can be reduced and/or avoided. Structures protected according to DIN EN 1995-2 have a service life of 60 - 80 years*.

* Source: Redemption amounts calculation regulations - ABBV, BMVBS, status 2010 and study of DGfH 2006

Advantages of the girder bridge:

• high cost-effectiveness due to simple construction type
• main girders are well protected against weathering
• optimum cross-section use for span widths of 5 to 20 m.
• simple railing connection possible
• road surface is designed with open timber decking or as sealed surface (e.g. with mastic asphalt) possible

References:

Here is a selection of laminated timber girder bridges.